Method for fluorinating a compound comprising a halosulphonyl or dihalophosphonyl group

ABSTRACT

The invention relates to a fluorination process for producing fluorinated compounds.  
     The process consists in reacting a compound (I) corresponding to the formula  
                 
 
     with an ionic fluoride of a monovalent cation. M represents H, an alkali metal, a quaternary phosphonium group or a quaternary ammonium group. Y represents SO 2  and m is 1, or else Y is PO and m is 2. Z represents CR 2 , N or P. R 1  represents an electron-withdrawing group which has a Hammet σ P  parameter of greater than 0.4. R 2  represents a carbonaceous and/or electron-withdrawing group. X represents a halogen other than a fluorine.  
     The fluorinated compounds obtained are of use in particular as electrolytes in lithium batteries.

[0001] The invention relates to a fluorination process for producingfluorinated compounds which can be used in particular as electrolyte.

[0002] Lithium batteries, in which the anode is formed by a sheet oflithium metal or by a lithium alloy and which operate by movement oflithium ions between the electrodes, have been widely studied. However,their development has been impeded due to the fact that, during theirrecharging, deposition of lithium metal of dendritic nature occurs,which can lead to short-circuits, resulting in an explosion in thesystem. This risk has been eliminated by replacing the lithium orlithium alloy anode by an anode composed of a carbonaceous material inwhich the lithium ions can be reversibly inserted. This novel form oflithium batteries, known as “lithium-ion” batteries, is widely used inthe field of portable electronic equipment. The electrolyte of thesebatteries comprises at least one lithium salt in solution in an organicsolvent which can be a polar aprotic liquid solvent (for example,ethylene carbonate, propylene carbonate or a dialkyl carbonate)optionally supported by a porous plastic support, a polar polymer [forexample, a crosslinked poly(ethylene oxide)] or a liquid solvent gelledby a polymer. The lithium salt plays an important role in the operationof the battery. The most widely used salt is LiPF₆, which makes itpossible to obtain liquid electrolytes which have a conductivity ofgreater than 10⁻² S.cm⁻¹ at ambient temperature. However, it has alimited thermal stability, which results in the formation of LiF and ofHF, said HF leading to decomposition of the electrolyte which can resultin an explosion in the battery. The lithium salt ofbis(trifluoromethanesulfonyl)imide has been envisaged for replacingLiPF₆, but it exhibits the disadvantage of resulting in depassivation ofthe aluminum current collector of the cathode.

[0003] The use of imide salts or methane salts having FSO₂ or F₂POelectron-withdrawing groups was then studied (WO 95/26056). These saltsmake it possible to obtain electrolytes with a greater conductivity thantheir homologues comprising perfluoroalkyl groups instead of thefluorine atoms and they result in markedly lower corrosion of thealuminum collectors. The use of an imide salt or methane salt comprisingFSO₂ or F₂PO groups thus makes it possible to maintain the low level ofcorrosion observed with LiPF₆ while improving the thermal stability withrespect to that of LiPF₆.

[0004] Various processes for the preparation of imide salts or methanesalts comprising at least one FSO₂ or F₂PO group have been described.For example, bis(fluorosulfonyl)imide (FSO₂)₂NH can be prepared byreaction of fluorosulfonic acid FSO₃H with urea H₂NC(O)NH₂. The imide issubsequently isolated by treatment of the reaction mixture with NaCl indichloromethane, followed by distillation of the pure acid [Appel &Eisenhauer, Chem. Ber., 95, 246-8, 1962]. However, the toxicity and thecorrosive nature of FSO₃H constitute a major disadvantage.

[0005] Another process consists in reacting (ClSO₂)₂NH with AsF₃. Theacid (FSO₂)₂NH is subsequently isolated by treating the reaction mixturewith NaCl in dichloromethane [Ruff and Lustig, Inorg. Synth., 1968, 11,138-43]. The disadvantage of this process lies in particular in the highcost of AsF₃, in its toxicity and in the risk of contaminating thecompound obtained.

[0006] For the phosphoryl derivatives, a process for the preparation ofLiN(POF₂)₂ consists in reacting LiN(SiMe₃)₂ with POF₃. The removal ofvolatile Me₃SiF results directly in the expected product [Fluck andBeuerle, Z. Anorg. Allg. Chem., 412(1), 65-70, 1975]. The disadvantageof this process lies in the cost of the silylated derivative and the useof gaseous and toxic POF₃.

[0007] It is known to prepare a fluorinated compound from thecorresponding halogenated compound by a halogen exchange reaction usingan ionic halide, such as, for example, KF or CsF, or an organicfluoride, such as tetra(n-butyl)ammonium fluoride. The reaction is anucleophilic substitution which preferably takes place in a polaraprotic solvent. The exchange reaction is promoted by the presence of aphase transfer catalyst chosen, for example, from quaternary ammoniumsalts, crown ethers, pyridinium salts or quaternary phosphonium salts.This process has been carried out with KF in particular to obtainmonofluoroalkanes, α-fluoroesters, fluoroethers, acyl fluorides orsulfonyl fluorides respectively from the corresponding monohaloalkanes,α-haloesters, haloethers, acyl halides or sulfonyl halides [A. Basbouret al. in M. Stacy and co-editors, Advances in Fluorine Chemistry, Vol.3, Butterworth, Washington D.C., 1963, pp. 181-250].

[0008] The inventors have now found that, surprisingly, thehalogen/fluorine exchange process can be employed for the fluorinationof various compounds comprising at least one halosulfonyl ordihalophosphoryl group attached to an atom carrying at least onestrongly electron-withdrawing substituent and optionally an acidichydrogen.

[0009] The aim of the present invention is consequently to provide aprocess for the fluorination of a compound comprising at least onehalosulfonyl or dihalophosphoryl group in which the halogen is otherthan a fluorine and at least one strongly electron-withdrawing group,for the purpose in particular of the preparation of the correspondingcompounds comprising at least one fluorosulfonyl or difluorophosphorylgroup.

[0010] The fluorination process according to the present inventionconsists in reacting, optionally in a solvent, a fluorinating agent witha compound (I) comprising a halosulfonyl [lacuna] substituent in whichthe halogen is other than a fluorine, wherein the fluorinating agent isan ionic fluoride of a monovalent cation and wherein the compound (I)corresponds to the following formula:

[0011] in which:

[0012] M represents H, an alkali metal, a quaternary phosphonium groupor a quaternary ammonium group;

[0013] Z represents CR², N or P;

[0014] Y represents SO₂ and m is 1, or else Y is PO and m is 2;

[0015] R¹ represents an electron-withdrawing group which has a Hammettσ_(P) parameter of greater than 0.4;

[0016] R² represents a carbonaceous and/or electron-withdrawing group;

[0017] X represents a halogen other than a fluorine.

[0018] The process is particularly preferred for the compounds in whichZ represents N.

[0019] The process is advantageously carried out at atmosphericpressure, at a temperature of less than 180° C. The temperature ispreferably less than 100° C., more particularly less than 80° C. Anexcessively slow reaction rate results from carrying out the process ata temperature below ambient temperature. The reaction medium can beheated by conventional means. Heating can also be carried out usingmicrowaves. Stirring the reaction medium or applying ultrasound is ofuse in replacing the active surface of the reactants when they are insuspension.

[0020] The monovalent ionic fluoride can be an alkaline fluoride or afluoride of a stable onium cation. Among alkali metals, it isadvantageous to use KF or CsF. Among onium cations, tetraalkylammonium,tetraalkylphosphonium or dialkylsulfonium cations are preferred. Oniumcations in which the alkyl radicals (which can be identical or differentin an onium cation) have from 1 to 12, more particularly from 1 to 4,carbon atoms are preferred. The abovementioned onium fluorides areadvantageous because of their high solubility in organic solvents. Theycan therefore be used alone or in combination with a less soluble ionicfluoride, for which they then act as charge transfer catalyst. When thecation M of the compound (I) is an alkali metal or an onium as definedabove for the fluoride, it is advantageous to use a fluoride of saidcation M. The use of LiF or of NaF, although giving relatively slowreactions, is advantageous when the fluorinated product obtained fromthe compound (I) is intended to be used as electrolyte. It is preferableto use an ionic fluoride having a high active surface.

[0021] The amount of ionic fluoride used with respect to the amount ofcompound (I) is preferably greater than stoichiometry. The ratio of thenumber of moles of fluoride to the number of halogen atoms to beexchanged of the compound (I) is advantageously from 1.1 to 2. When thecompound (I) is an imide [M is H in the formula (I)], said ratio ispreferably greater than 2, more particularly greater than 3.

[0022] The process of the present invention is particularly suitable forthe fluorination of compounds (I) in which M is H or an alkali metal,for example chosen from Na, K, Li or Cs. When M is a quaternary ammoniumor a quaternary phosphonium, it corresponds respectively to the formulaeN(R³R⁴R⁵R⁶) and P(R³R⁴R⁵R⁶) in which the various substituents R^(i) arechosen, independently of one another, from alkyl radicals preferablyhaving from 1 to 12, more particularly from 1 to 4, carbon atoms.

[0023] R¹ is an electron-withdrawing radical having a Hammett σ_(P)parameter of greater than 0.4. The radicals having a σ_(P) of greaterthan 0.5, more particularly of greater than 0.7, are particularlypreferred. Preferably, the radical R¹ does not carry a positive chargeat less than 6 chain members from Z. Mention may be made, as examples ofradicals R¹, of:

[0024] X′SO₂— and (X′)₂PO— radicals in which the group X′ represents orthe two groups X′ represent, independently of one another:

[0025] a halogen,

[0026] a R⁷CF₂— radical in which R⁷ is a halogen other than F or acarbonaceous radical preferably having at least 15 carbon atoms;

[0027] a perhalogenated radical R_(F), preferably having a number ofcarbon atoms of less than or equal to 15, corresponding to the formulaR⁸(CX″₂)_(p)— in which:

[0028] each of the X″ groups represents, independently of one another,F, Cl or a perfluoroalkyl radical having from 1 to 5 carbon atoms(preferably 2 carbon atoms), at least one of the X″ groups being F,preferably carried by the carbon connected to the sulfur, p being 1 or2;

[0029] R⁸ is an electron-withdrawing atom or radical having a σ_(p) ofgreater than 0 (preferably of greater than 0.1, more particularly ofgreater than 0.2), the possible functional groups of which are inertunder the reaction conditions, for example an F or a perfluoroalkylhaving at most 8 carbon atoms;

[0030] various radicals having a σ_(p) of greater than 0.4, mentioned inparticular in Advanced Organic Chemistry, 3rd Ed., Gerry March, p. 244,such as, for example, COOR′, COR′, SO₂R′, PO(R′)₂ or PO(OR′)₂ in whichR′ is preferably an alkyl radical having from 1 to 15 carbon atoms or anaryl radical having from 6 to 20 carbon atoms.

[0031] In a preferred embodiment, R¹— represents an X′SO₂— or (X′)₂PO—radical as defined above.

[0032] The substituent R² represents a carbonaceous and/orelectron-withdrawing radical. When R² is an electron-withdrawingradical, it is advantageously chosen from the nitrile radical and theradicals defined above for R¹. When R² is a carbonaceous group, it ispreferably chosen from radicals having from 1 to 20 carbon atoms.

[0033] When the compound (I) is liquid at the reaction temperature andwhen the ionic fluoride is soluble in said liquid compound, it is notessential to add a solvent to the reaction medium.

[0034] When the two reactants are in the solid form, the reaction iscarried out in a liquid solvent. The solvent is aprotic when M is otherthan H.

[0035] When the solvation of the cation of the monovalent fluoridereactant is desired, use is preferably made of a solvent having a donornumber from 10 to 30, preferably from 20 to 30. The donor number of asolvent represents the value −ΔH, ΔH being the enthalpy (in kcal/mol) ofthe interaction between the solvent and antimony pentachloride in adilute dichloromethane solution [cf. Christian Reinhardt, Solvent andSolvent Effects in Organic Chemistry, WCH, p. 19, 1988].

[0036] The solvents giving good results can in particular be amides,including amides with a specific nature, such as tetrasubstituted ureasand monosubstituted lactams. The amides are preferably substituted(disubstituted for ordinary amides). Mention may be made, for example,of pyrrolidone derivatives, such as N-methylpyrrolidone,N,N-dimethylformamide or N,N-dimethylacetamide. Another particularlyadvantageous category of solvents is composed of symmetrical orasymmetrical and open or closed ethers, including the variousderivatives of glycol ethers, such as glymes, for example diglyme. Thus,the most appropriate solvents, because of their cost and theirproperties, are advantageously chosen from ethers (in particular cyclicethers, such as THF, or polyfunctional ethers, such as glymes) or fromamides not having acidic hydrogen, such as DMF orN,N′-dialkyl-alkyleneureas, among which may be mentioned DMEU(N,N′-DiMethylEthyleneUrea) or DMPU (N,N′-DiMethylPropyleneUrea).Mention may also be made of N-methylpyrrolidone and cyclic ureasperalkylated on the nitrogens (e.g. DMEU or DMPU).

[0037] In addition, the solvent can be nitromethane.

[0038] It may be advantageous to add a phase transfer catalyst to thereaction medium, in order to improve the yield of the reaction. Thisaddition is particularly of use when the reaction is carried out in anonpolar or not very polar solvent. Mention may be made, as example ofphase transfer catalyst, of quaternary ammonium salts, crown ethers,pyridinium salts or quaternary phosphonium salts. The addition of aphase transfer catalyst is targeted at overcoming a relatively lowsolubility of the alkaline ionic fluoride used. A highly soluble ionicfluoride which can be used as fluorination reagent in the process of thepresent invention can be used as phase transfer catalyst when it iscombined with a fluoride reactant of low solubility. Mention may bemade, by way of example, of onium fluorides and cesium fluoride.

[0039] The compounds (I) can be prepared by processes of the prior art.An imide salt can be prepared by the action on the corresponding imideof a salt, the acid form of which is volatile under the reactionconditions. For example, the action of an alkaline hydride on an imidein a protic medium makes it possible to obtain an anhydrous imide salt.It is also possible to react an alkylmetal compound, for examplebutyllithium, with an imide, in order to obtain the corresponding imidesalt and an alkane, which is volatile if it is a lower alkane. Inaddition, it is possible to obtain an imide salt from the correspondingimide by exchange with a carboxylate with a sufficiently low molecularweight for the corresponding carboxylic acid to be volatile.

[0040] The present invention is illustrated by the following examples,to which, however, it is not limited.

EXAMPLE 1

[0041] 3.556 g (137.1 mM) of LiF were introduced into 5 ml ofnitromethane in a reactor and then the medium was stirred for 18 h inthe presence of glass beads. A solution of 4.907 g (0.22926 mM) ofbis(chlorosulfonyl)imide in 5 ml of nitromethane, corresponding to aLiF/imide molar ratio of approximately 6, was subsequently addeddropwise with stirring. The reaction was allowed to continue overnight.A solid residue separated by settling and the supernatant solution wasrecovered for analysis of the fluorine by NMR.

[0042] The analysis showed the presence of fluorine singlets at variouschemical shifts and with different peak heights: Chemical shift Peakheight Entity 56.6 1 FSO₂NH₂ 50.8 78.4 (SO₂F) (SO₂Cl)NH 54.5 12.7 SO₂F35.3 53.3 FSO₃ ⁻

[0043] After having continued the reaction for two weeks, different peakheights were obtained, the predominant compound being the desiredlithium bis(fluorosulfonyl)imide.

EXAMPLE 2

[0044] 4.111 g (19.205 mM) of bis(chlorosulfonyl)imide were dissolved in5 ml of nitromethane. 6.549 g (155.97 mM) of finely divided NaF wereadded at 0° C. with continuous stirring. The NaF/imide molar ratio is ofthe order of 8. The reaction mixture was allowed to rise to ambienttemperature and then was stirred in the presence of 3 glass beads for 60h. After separation by settling, fluorine NMR analysis of the clearsupernatant solution showed the presence of the desired product.

EXAMPLE 3

[0045] 4.361 g (75.06 mM) of KF were suspended in 5 ml of nitromethaneand then a solution of 3.176 g (14.84 mM) of bis(chlorosulfonyl)imide in3 ml of nitromethane was introduced with continuous stirring. TheKF/imide molar ratio is of the order of 5.

[0046] The reaction mixture heated up and the reactor was stirred withglass beads for 14 h. 3.49 g (60.034 mM) of fresh KF were then added andthe mixture was stirred for a further 18 h. The solution became deeporange. After separating the solid particles by settling, the fluorineNMR analysis was carried out, which showed that the predominant productexhibits a chemical shift (singlet) of 51.6 ppm and corresponds to theconversion of 99% of the starting product. The predominant productobtained is potassium bis(fluorosulfonyl)imide.

[0047] The procedure of this example was employed in three additionaltests, using, instead of bis(chlorosulfonyl)imide, φSO₂NHSO₂Cl,CF₃SO₂NHSO₂Cl and (φSO₂)₂CHSO₂Cl respectively, and the predominantformation of the following compounds was observed: φSO₂NKSO₂F (fromφSO₂NHSO₂Cl), CF₃SO₂NKSO₂F (from CF₃SO₂NHSO₂Cl) and (φSO₂)₂CKSO₂F from(φSO₂)₂CHSO₂Cl.

EXAMPLE 4

[0048] 4.421 g (29.104 mM) of CsF were dispersed in 2 ml of nitromethanewhile stirring with glass beads. A solution of 2.243 g (10.480 mM) ofbis(chlorosulfonyl)imide in 5 ml of nitromethane was added dropwise withstirring. The CsF/imide molar ratio is of the order of 3. After areaction time of 72 h, followed by stirring for 6 h, fluorine NMRanalysis of the supernatant liquid showed the following lines: Chemicalshift Peak height Entity 56.5 15.5 FSO₂NH₂ 52.1 48.3 (SO₂F) (SO₂Cl)N⁻51.9 225.6 [N(SO₂F)²]⁻

[0049] It thus emerges that 80% of the starting imide has been convertedto bis(fluorosulfonyl)imide.

EXAMPLE 5

[0050] Bis(dichlorophosphoryl)imide was reacted with KF by a processanalogous to that described in example 3. It was found that theconversion of the starting material with a yield of 90% and thepredominant formation of potassium bis(difluorophosphoryl)imide.

[0051] Bis(dichlorophosphoryl)imide can be prepared according to theprocess described by Riesel et al. [Riesel, Pfuetzner & Herrmann, Z.Chem., 23(9), 344-5, 1983].

What is claimed is:
 1. A process for the fluorination of a compound (I)comprising at least one halosulfonyl or dihalophosphoryl group in whichthe halogen is other than a fluorine and at least one stronglyelectron-withdrawing group, which consists in reacting, optionally in asolvent, a fluorinating agent with said compound, wherein thefluorinating agent is an ionic fluoride of a monovalent cation andwherein the compound (I) corresponds to the following formula:

in which: M represents H, an alkali metal; a quaternary phosphoniumgroup or a quaternary ammonium group; Z represents CR², N or P; Yrepresents SO₂ and m is 1, or else Y is PO and m is 2; R¹ represents anelectron-withdrawing group which has a Hammett σ_(P) parameter ofgreater than 0.4; R² represents a carbonaceous and/orelectron-withdrawing group; X represents a halogen other than afluorine.
 2. The process as claimed in claim 1, which is carried out atatmospheric pressure.
 3. The process as claimed in claim 1, which iscarried out at a temperature of less than 180° C.
 4. The process asclaimed in claim 1, wherein the monovalent ionic fluoride is KF or CsF.5. The process as claimed in claim 1, wherein the monovalent ionicfluoride is tetraalkylammonium, tetraalkylphosphonium ordialkylsulfonium fluoride.
 6. The process as claimed in claim 5, whereinthe alkyl groups of the cation of the monovalent fluoride have from 1 to12 carbon atoms.
 7. The process as claimed in claim 1, wherein the ratioof the number of moles of fluoride to the number of halogen atoms to beexchanged of the compound (I) is greater than
 1. 8. The process asclaimed in claim 7, wherein the ratio of the number of moles of fluorideto the number of halogen atoms to be exchanged of the compound (I) isfrom 1.1 to
 2. 9. The process as claimed in claim 7, wherein the ratioof the number of moles of fluoride to the number of halogen atoms to beexchanged of the compound (I) is greater than 2 when M is H.
 10. Theprocess as claimed in claim 1, wherein M represents H, an alkali metal,a quaternary ammonium N(R³R⁴R⁵R⁶) or a quaternary phosphoniumP(R³R⁴R⁵R⁶), the various substituents R^(i) being chosen, independentlyof one another, from alkyl radicals preferably having from 1 to 12carbon atoms.
 11. The process as claimed in claim 1, wherein the cationM is identical to the cation of the monovalent fluoride.
 12. The processas claimed in claim 1, wherein R¹ is an electron-withdrawing grouphaving a Hammett σ_(P) parameter of greater than 0.7.
 13. The process asclaimed in claim 1, wherein R¹ and/or R² are an X′SO₂— or (X′)₂PO—radical in which X′ represents: a halogen, an R⁷CF₂— radical in which R⁷is a halogen other than F or a carbonaceous radical; a perhalogenatedradical R_(F), corresponding to the formula R⁸(CX″₂)_(p)— in which: eachof the X″ groups represents, independently of one another, F, Cl or aperfluoroalkyl radical having from 1 to 5 carbon atoms, at least one ofthe X″ groups being F, p being 1 or 2; R⁸ is an electron-withdrawingatom or radical having a σ_(p) of greater than 0, the possiblefunctional groups of which are inert under the reaction conditions. 14.The process as claimed in claim 13, wherein R⁷ is a carbonaceous radicalhaving at most 15 carbon atoms.
 15. The process as claimed in claim 13,wherein at least one of the X″ groups represents a perfluoroalkylradical having from 1 to 5 carbon atoms.
 16. The process as claimed inclaim 13, wherein at least one of the X″ groups is a F atom carried bythe carbon connected to the sulfur.
 17. The process as claimed in claim13, wherein R⁸ is F or a perfluoroalkyl radical having at most 8 carbonatoms.
 18. The process as claimed in claim 1, wherein R¹ represents aCOOR′, COR′, SO₂R′, PO(R′)₂ or PR(OR′)₂ radical in which R′ is an alkylradical having from 1 to 15 carbon atoms or an aryl radical having from6 to 20 carbon atoms.
 19. The process as claimed in claim 1, wherein R²is a nitrile or a carbonaceous radical having from 1 to 20 carbon atoms.20. The process as claimed in claim 1, which is carried out in anaprotic solvent.
 21. The process as claimed in claim 1, wherein thesolvent is nitromethane.
 22. The process as claimed in claim 1, which iscarried out in a solvent chosen from substituted or unsubstituted amidesand symmetrical or asymmetrical and cyclic or noncyclic ethers.
 23. Theprocess as claimed in claim 1, wherein the reaction medium comprises aphase transfer catalyst.